The behavior can be observed with the following setups:

new WmsTiledProvider("http://4maps.geo-solutions.it/geoserver/osm/wms")

            {
                Layers = "osm",
                Version = "1.3.0",
                Projection = "CRS:84" // WGS84, 1.3.0 Standard compatible
            };

and 

new WmsTiledProvider("http://4maps.geo-solutions.it/geoserver/osm/wms")

            {
                Layers = "osm",
                Version = "1.1.0",
                Projection = "EPSG:4326" // WGS84, 1.1.0 Standard compatible
            };